10Root-associated microbial communities influence plant phenotype, growth and local abundance, 11 yet the factors that structure these microbial communities are still poorly understood. California 12 landscapes contain serpentine soils, which are nutrient-poor and high in heavy metals, and 13 distinct from neighboring soils. Here, we surveyed the rhizoplane of serpentine-indifferent plants 14 species growing on serpentine and non-serpentine soils to determine the relative influence of 15 plant identity and soil chemistry on rhizoplane microbial community structure using 16S rRNA 16 metabarcoding. Additionally, we experimentally examined if locally adapted microorganisms 17 enhance plant growth in serpentine soil. Plant species, soil chemistry, and the interaction 18 between them were important in structuring rhizoplane bacterial communities in both the field 19 and experimental soils. In the experiment, rhizoplane microbial community source influenced 20 seedling survival, but plant growth phenotypes measured were largely invariant to microbial 21 community with a few exceptions. Results from the field sampling suggest that plant species 22 associate with specific microbial communities even across chemically distinct soils, and that 23 microbial communities can differentially influence seedling survival on harsh serpentine soils. 24 Words: 169 25Importance 26Microbial communities on plant roots can influence host plant phenotype, survival, and fitness, 27 with community and ecosystem consequences. However, which factors structure microbial 28 community structure is poorly understood, particularly across large gradients in soil properties. 29The survey and experiment described here shows that plant species host distinct microbiomes 30 despite strong turnover in soil chemistry, although soil type also influences bacterial structure. 31These results suggest that host specificity and soil conditions are both strong drivers of 32 rhizoplane bacterial composition in serpentine ecosystems and influence plant seedling 33 establishment. These results imply that plant species can recruit relatively convergent 34 microbiomes from distinct microbial communities found on different soil types and that soil 35 microbial communities influence seedling establishment. 36 37 38 39 Plant collection 131Plantago erecta, T. fucatum, C. sparsiflora and G. tricolor were collected from two geographically 132